1. Field of the Invention
The present invention relates to a display device, and more particularly, to a technique of connecting terminals to an IC driver or the like when the terminal pitch is small due to the reduced size of the display device, or enhanced screen resolution, or the reduced size of the IC driver.
2. Description of the Related Art
In liquid crystal displays, a liquid crystal is held between a TFT substrate and an opposite substrate, with pixel electrodes, thin-film transistors (TFTs), and others formed into a matrix pattern on the TFT substrate and pigment dots of a color filter and others formed on the opposite substrate in places that correspond to the locations of the pixel electrodes. Liquid crystal displays form an image by controlling the light transmittance for each pixel separately by controlling liquid crystal molecules.
Multiple video signal lines running in the longitudinal direction of the TFT substrate are arranged in the lateral direction of the TFT substrate, whereas multiple scanning lines running in the lateral direction of the TFT substrate are arranged in the longitudinal direction of the TFT substrate. A pixel is formed in a region enclosed by the video signal lines and the scanning lines. The major components of each pixel are a pixel electrode and a thin-film transistor (TFT), which is a switching element. Numerous pixels formed into a matrix pattern in this manner constitute a display area. In the display area of the TFT substrate, TFTs are formed first, then an inorganic passivation film is formed on the TFTs, and pixel electrodes are formed on the passivation film. An insulating film such as an SiN film is used as the inorganic passivation film, and a transparent conductive film such as an ITO film is used as the pixel electrodes.
Components formed outside the display area of the TFT substrate include a group of terminals for supplying video signals to the video signal lines and a group of terminals for supplying scanning signals to the scanning lines. Bumps formed in an IC driver (driver chip) are connected to these terminal groups. As the screen resolution is higher, more terminals are connected to the IC driver and the pitch between terminals is smaller. A reduction in bump pitch as a result of the downsizing of the IC driver also contributes to a narrower terminal pitch. With the terminal pitch reduced, securing enough area for connecting the terminals to the bumps formed in the IC driver is difficult. Japanese Patent Application No. 2006-193987 (Japanese Patent Application Laid-open 2008-20791) describes a structure in which, when the wiring pitch is smaller than the bump pitch of an IC driver, the bump pitch and the wiring pitch are made compatible with each other by connecting wiring lines and bumps in several stages.
When a display device is reduced in size causing a framing area around the display area to be smaller, lead-out lines of scanning lines, in particular, are gathered to one side of the display device. If all the lead-out lines of scanning lines are to be laid on a single plane in this case, a large area is needed. In order to avoid this problem, leading out the lead-out lines of scanning lines three dimensionally through an insulating layer requires less area for the lead-out lines of scanning lines. This structure is described in, for example, Japanese Patent Application Laid-open 2004-053702.
In the process of manufacturing a liquid crystal display device, the step of assembling a liquid crystal display panel includes checking for short circuit and other defects in wiring lines that are formed on the liquid crystal display panel before an IC driver is installed in the liquid crystal display panel. If short circuit and other wiring defects are found at this stage, there is no sense in performing the subsequent steps on the defective liquid crystal display panel, and the manufacturing cost can thus be lowered. TFT switches and the like are therefore placed in an area that is outside the display area and that is close to terminals to be connected to the IC driver. A liquid crystal display device structure as this that allows for the checking step is described in Japanese Patent Application No. 2006-181249 (Japanese Patent Application Laid-open 2008-9246).
Further enhancement of the display device resolution, narrowing of the frame, and downsizing of IC drivers will make the wiling pitch even smaller. In liquid crystal and other display devices, wiring lines outside the display area are covered with an insulating film such as the passivation film as a protection against the outside air. The wiring lines, however, need to be exposed in places where the wiring lines are connected to the bumps of the IC driver or the like, by forming contact holes in the insulating film. The contact holes are covered with a transparent conductive film that is chemically stable, for example, an ITO film, in order to avoid the corrosion of the wiring lines in the contact holes.
A given area is necessary to form a contact hole. Also, a given contact area is needed in order to ensure a reliable connection between a terminal and a bump. The enough era for the contact holes or the contact area for the bump-terminal connection can be secured by arranging the terminals in a staggered pattern, or by arranging the terminals in rows as described in Japanese Patent Application No. 2006-193987 (Japanese Patent Application Laid-open 2008-20791). However, arranging the terminals in these manners narrows the areas of other wiring lines running in parallel to the wiring lines of the terminals, possibly to a degree that makes the wiring width and the wiring interval smaller than the precision of wiring machining.